Improvement in perspective t-squares



E. M. HAMILTON. Perspective T-Square'.

No. 222,271. Patented Dec. 2, 1879.

WITNESSES INVENTOR 61W 62 4 6 m H a TORNEYS.

N. PEI'EHS. FHOTO-LITHOGRARHER. WASHINGTON. D c,

EMERY M. HAMILTON, or

UNITED-STATES PATENT oat-ice.

NEW YORK, N. Y., ASSIGNOR TO 0. T.RAYNOLDS & 00., OF SAME PLACE.

IMPROVEMENT IN PERSPECTIVE T-SQUARES.

Specification forming part of Letters Patent No. 222.271, dated December2, 1879; application filed September 20, 1879.

To all whom it may concern:

Be it known. that I, EMERY M. HAMILTON, of the city, county, and Stateof New York, have invented a new and Improved Perspective T-Square,ofwhich the following is aspecification.

The object of my invention is tofurnish a T-square for use in makingperspective drawings, whereby the mechanical difficulties connected withsuch work may be readily overcome. Heretofore in making such drawings,to avoid the tedious process of working by diagonals or by elaboratescales, whereby only an accurate perspective could be obtained, thedraftsman has usually made the vanishingpoint too close,so asto bring itwithin reach, or has selected a point of view with reference to theangle thatwill effect the same object, the result in either case beingto cramp or distort the drawing.

My invention consists in an improved T- square, fitted with a swingingblade, adapted for giving perspective lines vanishing either to theright or left at any distance, which blade is moved by an adjustableslide-piece, that is attached upon the drawing-board, whereby a true andaccurate perspective drawing may be made with facility.

The construction and operation will be explained with reference to theaccompanying drawings, and the invention pointed out in the claims.

In the drawings, Figure 1 is a plan view of drawing-board with myimproved T-square applied thereto. Fig. 2 is a cross-section of the sameon line w w of Fig. 1. Fig. 3 is an inverted plan view of the T-squarehead. Fig. 4 is a section of the head on line 3 y of Fig. 3.

Similar letters of reference indicate corresponding parts.

A is a drawing-board of usual character, fitted with the adj List-ableslide, as hereinafter described 5 and B is the improved T-square,'ofwhich a is the head and b the blade. The head a of the square B is to bemade of hard rubber or other suitable material, with a flange, a, totake against'the edge of board A, and is recessed on the under side toreceive the end of blade I) and its operating mechanism, so that thehead may lie flat upon the board A. Within this recess of the head a isa cogged segment, 0, having a tubular hub, into which the screw d entersfrom the upper side of the head, so that the segment a is securely heldand may turn freely. Upon one side of segment 0 is an arm, 0, the outerend of which is slotted to sit over a pin, f, projecting. from aslide-block, d, that is fitted in a dovetail groove in the metal piece0, which is attached to head a. To the arm 0 the blade bis rigidlyattached, with its upper edge in line with theaxis of segment 0, andpreferably extendingat a right angle with a line through the center ofaxis d and pin f. Upon a screw-stud at. the under side of head a smallgear-wheel, g, is fitted, meshing with segment a, and fitted at itsunder side, as shown in Fig. 4:, with a coiled spring, h, that isfastened to the stud and to the wheel g, so that the spring tends tothrow the outer end of blade I) downward.

It will be seen that by this construction the slide-block (1-, blade b,segment 0, and wheel 9 all move together, and that the line described bythe upper edge of blade I) is always radial to the axis of segment 0.The bladeb lies flush with the under surface of head a, and its movementin either direction is limited by the sides of the recess in which itmoves.

Upon the board A, near the edge,'a strip, 6, of metal is attached by ascrew or pin, 41, that permits a swinging movement of the strip. In theupper end of the strip '5 is a slot or mortise, 70, adapted forreceiving the end of any one of the swinging stops I. These stopsl areattached to board aby screws l, passing through slots in the stops, andserve to hold the strip riinits position as adjusted more or lessinclined to the edge of board A, either stop being used; and Ihave shownthe stops l as provided with a small aperture, through which athumb-tack may be inserted into board A to hold the parts more securely.I

The strip i is formed with a shoulder or flange, 12:, extendinglengthwise, against which the pin f of the slide-block d bears when theT-square is in place.

A slat or other equivalent device may be used in place of shoulder m;but I prefer the shoulder. The end of board A is recessed to receive theslide 1' and stops 1, so that the head of the T-square may lie flat uponthe board over the slide.

In use the angle of the blade I) to the head a is regulated by the slide1', and the adjustment is made by moving the slide z'to the right togive lines vanishing a greater or less distance to the left, and movingit to the left to give lines vanishing to the right. By these means theT-square permits perfect freedom in making a perspective drawing, as thevanishing-point may be more or less distant, as required, to obtain atrue efl'ect.

The T-square is also adapted for use as an ordinary square, the slide iin that case being set parallel with the edge of the hoard, and the heada will remain in place without being held by hand.

Having thus described my invention, what I claim as new, and desire tosecure by Letters Patent, is-

1. The improved perspective T-square, consisting of the swinging bladeI), pivoted to the head a, and connected with the slide-block d,

in combination with the adjustable guidepiece 6 upon the drawing-board,substantially as described and shown.

2. In a perspective T-square, the segment 0, pivot-screw d, slotted arma, slide d, pin f, and blade 11, combined together and with the head a,substantially as and for the purpose set forth.

3. In a perspective T-square, the combination, with the swinging segmenta, carrying the blade 0, of the wheel g and spring h, substantially asdescribed and shown, and for the purposes set forth.

4. In combination with the T-square fitted with a swinging blade,substantially as described, the guidestrip 2', formed with a shoulder,and fitted to swing upon its attachment to the drawing-board,substantially as and for the purposes specified.

5. In combination with the guide-strip i, the swinging stops 1,substantially as and for the purposes set forth.

EMERY M. HAMILTON.

Witnesses:

Gee. I). WALKER, (J. SEDGWICK.

